SIZE_DATA_BUFFERS Recommended Values

[sgoldsmith]

Hi All (been a while!!),

SIZE_DATA_BUFFERS - Does anyone have an information on what this value should be set to for different tape drive / controller cards?

I know that the value should not be greater than the maximum tape drive I/O block size, but what is that for different drive technologies?

For example I know that we set 256k (262144) for most of our tape drives,but that is from 9840B drives right the way up to LTO3. However, I can't believe that LTO3 drive is still limited to 256k block size.

Simon

P.S We are using all fibre channel drives so the block size issue with older SCSI based controller doesn't effect us.

Simon Goldsmith
Storage Engineer

 

[Stumpr]

Have you seen the FAQ written by PGPhantom
javascriptpenindex(450,450,'

http://www.tipmaster.com/includes/refinfo.cfm?w=450&h=450')

Bob Stump
Just because the VERITAS documentation states a certain thing does not make it a fact and that is truth.

 

[Stumpr]

hmmm that link didn't work so great.

faq776-3984



Bob Stump
Just because the VERITAS documentation states a certain thing does not make it a fact and that is truth.

 

[Stumpr]

There is also information in

VERITAS NetBackup (tm) Enterprise Server / Server 6.0 Backup Planning and Performance Tuning Guide for UNIX, Windows, and Linux

http://seer.support.veritas.com/docs/281842.htm

Bob Stump
Just because the VERITAS documentation states a certain thing does not make it a fact and that is truth.

 

[sgoldsmith]

Bob,

Thanks for the link.. the NB 6 tuning guide is something I have read and studied before, but PGPhantom's doc is useful... however, it still doesn't really answer the question.

Veritas state:

IMPORTANT: Because the data buffer size equals the tape I/O size, the value specified in SIZE_DATA_BUFFERS must not exceed the maximum tape I/O size supported by the tape drive or operating system. This is usually 256 KB or 128 KB.

That means that the BUFFER SIZE should only ever be up to or equal to the tape drives max I/O block size. The other 2 tuning Variables (NET_BUFFER_SZ - network buffers and NUMBER_DATA_BUFFERS) are the "changable" ones (determined based on the performance of your system - CPU, available memory etc).

So, again, I can't believe that the max tape I/O block size is the same across all tape drives and manafactures or that it hasn't changed as tape technology moves forward!

Any thoughts / more information?

Simon Goldsmith
Storage Engineer